added info/link for ansible-lockdown to mailing list section, minor editing
(can't help myself it seems) to the paragraph about subscribing from a non-google account

fixes #12104

Vault cleanups, pass #1

Synchronize fix error

Now we don't have to recreate VaultEditor objects for each file, and so
on. It also paves the way towards specifying separate input and output
files later.

It's unused and unnecessary; VaultLib can decide for itself what cipher
to use when encrypting. There's no need (and no provision) for the user
to override the cipher via options, so there's no need for code to see
if that has been done either.

Fix the error:
 "RuntimeError: dictionary changed size during iteration"

Fixes #11981
Fixes #11995
Fixes #12039
Fixes #12077

also normalized -M option across all cli
fixes #12016

This bug was introduced in commit f8bf2ba1 on July 27.  Hasn't gone out
in a release yet.

Unicode and other fixes for vault

add option to ansible-vault to read new password from file for rekey

allow ansible to connect to docker containers (without using ssh)

The --new-vault-password-file option works the same as
--vault-password-file but applies only to rekeying (when
--vault-password-file sets the old password). Also update the manpage
to document these options more fully.

remove defaults from inhertiable fieldattributes to allow for proper detection and override

added block environment test

Speed up execution

`if method in dir(self):` is very inefficient:

- it must construct a list object listing all the object attributes & methods
- it must then perform a O(N) linear scan of that list

Replace it with the idiomatic `if hasattr(self, method):`, which is a
O(1) expected time hash lookup.

Should fix #11981.

fixes #12055